Change merging rule

pkg/document/crdt/tree.go

@@ -602,10 +602,16 @@ func (t *Tree) Edit(from, to *TreePos,
 
 			// NOTE(hackerwins): If the node overlaps as an opening tag with the
 			// range then we need to move the remaining children to fromParent.
-			// TODO(hackerwins): Define more clearly merge-able rules between fromParent
-			// and toParent. For now, if fromParent and toParent are the same
-			// type, then we can merge them.
-			if !node.IsText() && contain == index.OpeningContained && fromParent.Type == toParent.Type {
+			if !node.IsText() && contain == index.OpeningContained {
+				// TODO(hackerwins): Define more clearly merge-able rules
+				// between two parents. For now, we only merge two parents are
+				// both element nodes having text children.
+				// e.g. <p>a|b</p><p>c|d</p> -> <p>a|d</p>
+				if !fromParent.Value.IndexTreeNode.HasTextChild() ||
+					!toParent.Value.IndexTreeNode.HasTextChild() {
+					return
+				}
+
 				for _, child := range node.IndexTreeNode.Children() {
 					if slices.Contains(toBeRemoveds, child.Value) {
 						continue

pkg/document/crdt/tree_test.go

@@ -210,7 +210,7 @@ func TestTree(t *testing.T) {
 		assert.Equal(t, 2, node.Children[0].Size)
 		assert.Equal(t, 2, node.Children[0].Children[0].Size)
 
-		// 02. Delete b from the first paragraph.
+		// 02. Delete b from the second paragraph.
 		// 	     0   1 2    3   4 5 6    7
 		// <root> <p> a </p> <p> c d </p> </root>
 		_, err = tree.EditByIndex(2, 3, nil, nil, helper.IssueTime(ctx))
@@ -244,7 +244,7 @@ func TestTree(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, "<root><p>ab</p><p>cd</p></root>", tree.ToXML())
 
-		// 02. delete b, c and first paragraph.
+		// 02. delete b, c and the second paragraph.
 		//       0   1 2 3    4
 		// <root> <p> a d </p> </root>
 		_, err = tree.EditByIndex(2, 6, nil, nil, helper.IssueTime(ctx))
@@ -264,6 +264,33 @@ func TestTree(t *testing.T) {
 		assert.Equal(t, "<root><p>@ad</p></root>", tree.ToXML())
 	})
 
+	t.Run("delete nodes between element nodes in different levels test", func(t *testing.T) {
+		// 01. Create a tree with 2 paragraphs.
+		//       0   1   2 3 4    5    6   7 8 9    10
+		// <root> <p> <b> a b </b> </p> <p> c d </p>  </root>
+
+		ctx := helper.TextChangeContext(helper.TestRoot())
+		tree := crdt.NewTree(crdt.NewTreeNode(helper.IssuePos(ctx), "root", nil), helper.IssueTime(ctx))
+		_, err := tree.EditByIndex(0, 0, nil, []*crdt.TreeNode{crdt.NewTreeNode(helper.IssuePos(ctx), "p", nil)}, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		_, err = tree.EditByIndex(1, 1, nil, []*crdt.TreeNode{crdt.NewTreeNode(helper.IssuePos(ctx), "b", nil)}, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		_, err = tree.EditByIndex(2, 2, nil, []*crdt.TreeNode{crdt.NewTreeNode(helper.IssuePos(ctx), "text", nil, "ab")}, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		_, err = tree.EditByIndex(6, 6, nil, []*crdt.TreeNode{crdt.NewTreeNode(helper.IssuePos(ctx), "p", nil)}, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		_, err = tree.EditByIndex(7, 7, nil, []*crdt.TreeNode{crdt.NewTreeNode(helper.IssuePos(ctx), "text", nil, "cd")}, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		assert.Equal(t, "<root><p><b>ab</b></p><p>cd</p></root>", tree.ToXML())
+
+		// 02. delete b, c and the second paragraph.
+		//       0   1   2 3 4    5
+		// <root> <p> <b> a d </b> </root>
+		_, err = tree.EditByIndex(3, 8, nil, nil, helper.IssueTime(ctx))
+		assert.NoError(t, err)
+		assert.Equal(t, "<root><p><b>ad</b></p></root>", tree.ToXML())
+	})
+
 	t.Run("style node with element attributes test", func(t *testing.T) {
 		// 01. style attributes to an element node.
 		ctx := helper.TextChangeContext(helper.TestRoot())

pkg/index/tree.go

@@ -569,8 +569,8 @@ func (n *Node[V]) InsertAfter(newNode, referenceNode *Node[V]) error {
 	return nil
 }
 
-// hasTextChild returns true if the node has a text child.
-func (n *Node[V]) hasTextChild() bool {
+// HasTextChild returns true if the node has a text child.
+func (n *Node[V]) HasTextChild() bool {
 	for _, child := range n.Children() {
 		if child.IsText() {
 			return true
@@ -765,7 +765,7 @@ func (t *Tree[V]) PathToTreePos(path []int) (*TreePos[V], error) {
 		}
 	}
 
-	if node.hasTextChild() {
+	if node.HasTextChild() {
 		return findTextPos(node, path[len(path)-1])
 	}
 	if len(node.Children()) < path[len(path)-1] {